Biometrics is commonly used to identify and/or authenticate individuals based on individual physical characteristics.
Such an identification via biometrics, implemented by a biometric authentication system, comprises the three following main steps:                capturing of a reference biometric sample coming from the authorized individual (for example a reference image of an authorized individual);        creation of a reference file, or “reference signature” (which comprises at least one characteristic element of the reference image), by a specific treatment applied to the reference biometric sample, then storage of this reference file;        verification wherein, in the same way as with the aforementioned steps of capturing and of creating, a capture of a biometric sample to be compared coming from the individual to be authenticated and the creation of a file to be compared, or “signature to be compared” are carried out, then a comparison of the reference file with the file to be compared in order to determine their rate of similarity and take the decision that is required is achieved.        
As such, the information stored is not biometric samples, but mathematical models of these samples that distinguish one biometric sample from another. This model is called a “signature” or a “template”.
The creation of a reference signature is carried out during a phase referred to as enrolment (or learning) that groups together the steps of capturing the reference biometric sample, creating and storing the reference signature and storing the information on the identity of the individual such as his last name, first name, identifier (personal identification number).
The authentication of an individual via biometrics can in particular be based on the measurement (or capture) of at least one of the following biometric samples, or a combination of one or several of the following biometric samples:                his fingerprint;        his palm print (hand print);        the print of his retina;        the print of his iris;        the print of his face (the facial shape);        . . .        
A disadvantage of these biometric authentication systems of prior art lies in their slowness when they are used to reference a large number of individuals (for example to control the access to the underground in a large city or to authenticate a user of a bank card).
Indeed, the duration of the step of verification, during which the authentication decision properly speaking is taken, depends on the number of referenced individuals in the authentication system. The more referenced individuals there are, the higher the number of potential comparisons to be made in order to determine or not determine the authentication of an individual is.
As such, the higher the number of referenced individuals is, the slower the system is.
Another disadvantage of these biometric authentication systems of prior art lies in the increasing risk of authentication errors according to the number of referenced individuals.
Indeed, the higher the number of referenced individuals is, the more the system is likely to reference several pieces of close biometric information, each corresponding to different individuals. Then, during the authentication phase, such a system has a greater risk of authentication errors, due to this proximity of the biometric information referenced for different individuals.